Work continues on the mechanism of reactions requiring coenzyme B12, specifically propanediol dehydrase. Investigations of three kinds are being carried out: (1) kinetic and product studies of fluorinated substrate analogues stereospecifically deuterated at various positions, (2) esr examination of possible radical intermediates, (3) attempts to isolate cobalamine-substrate intermediates. Studies of serine proteases concentrate on understanding the behavior of the catalytic triad of these enzymes, specifically through studies of binding, as a function of pH, of aldehydes to alpha-lytic protease to give analogues of the tetrahedral intermediate. Magnetic resonance studies of specifically 13C labeled soybean inhibitor interacting with trypsin are also underway. BIBLIOGRAPHIC REFERENCE: Mechanism of Serine Protease Action. Ionization Behavior of Tetrahedral Adduct Between Alpha-Lytic Protease and Tripeptide Aldehyde Studied by 13C Magnetic Resonance, Michael W. Hunkapiller, Stephen H. Smallcombe and John H. Richards, Org. Magnetic Resonance, 7, 262 (1975).